The invention relates to a magnet rotor used for a light quantity adjustment device and as a drive source of an electromagnetic drive device used for the light quantity adjustment device. The device typically adjusts photographic light quantity or projecting light quantity by open/closed driving blade members such as a shutter blade, diaphragm blade and the like in optical equipment such as imaging devices like a still camera, video camera and so on, or projecting devices like a rear projection television, a front projector and so on.
Generally, this kind of light quantity adjustment device adjusts light quantity passing through an optical path by arranging a blade member in the optical path and by opening/closing the blade member by an electromagnetic drive device. The electromagnetic drive device includes a magnet rotor in which a rotary shaft is provided at the center of a permanent magnet and a stator in which an excitation coil is wound around a periphery of a coil frame. The magnet rotor is rotated to a predetermined angle by turning on electricity to the excitation coil, to open/close the blade member.
As the magnet rotor used for the above-described electromagnetic drive device, one in which a rotary shaft of a drive arm is pressed into a central through hole of a permanent magnet to be united with each other as disclosed in JP-A-8-19239, one in which a rotary shaft is bonded to a permanent magnet by an adhesive to be united with each other as disclosed in JP-A-9-56092, and further one in which molding material such as resin is inserted into a magnet having a hollow cylindrical shape to be united with each other as disclosed in JP-A-6-258683 and the like are known.
These methods for uniting the magnet rotor are used respectively according to the compatibility to certain devices, and the present application relates to an adhesion method among these methods.
In the past, in the adhesion method, two-component epoxy resin has been used in general for an adhesive thereof. The reason why the two-component epoxy resin has been used is that, first, it is easy to deal with because the curing starts by mixing the adhesive with a curing agent when using the adhesive. Secondly, the adhesive has a long curing time and is not cured during a positioning time which is required for positioning a direction of the drive arm and a direction of an axis of easy magnetization of the permanent magnet to a prescribed relation in the magnet rotor. As a result, the two-component epoxy resin is suitable for use as an adhesive of the magnet rotor.
One-component epoxy resin is also known as an adhesive. However, the one-component epoxy resin is cured by being exposed to air. The adhesive applied between the rotary shaft of the drive arm and the central through hole of the permanent magnet is difficult to cure since it is hardly exposed to air, therefore, the resin is not regularly used.
However, the above two-component epoxy resin is used by mixing the adhesive with the curing agent. When used, therefore, there arose problems such as adhesion failure of curing spots caused by a poor mixing state. Additionally, there was rotation failure caused by adhesive flowing out of a bearing portion of the rotary shaft as a result of the long curing time, such as in the case of adhesive being applied between the rotary shaft of the drive arm and the central through hole of the permanent magnet when a device diameter becomes small in accordance with miniaturization.
An object of the invention, therefore, is to provide a magnet rotor, an electromagnetic drive device and a light quantity adjusting device using the magnet rotor. According to the invention, in manufacturing the magnet rotor, the adhesive is not mixed with a curing agent as in the conventional way, and curing start time can be controlled. Secondly, after the curing starts, the resin is cured immediately with no leakage, even in a sealed portion, and it is securely cured without curing spots.
Further objects and advantages of the invention will be apparent from the following description of the invention.